Clay additive for reduction of sulfur in catalytically cracked gasoline

ABSTRACT

Compositions and processes for their use as additives for reducing the sulfur content of FCC gasoline employ a support material montmorillonite clay material. A fluid catalytic cracking (FCC) mixture, therefore, is provided comprising an FCC catalyst and separate particles of sulfur reduction additive consisting of porous montmorillonite clay.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.12/462,338 filed on Jul. 30, 2009, which is related to and claimspriority from U.S. Provisional Patent Application Ser. No. 61/137,471filed on Jul. 30, 2008, and is a Continuation-in-Part of U.S.application Ser. No. 11/477,275 filed on Jun. 28, 2006, which are bothincorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the reduction of sulfur in gasoline producedin a fluid catalytic cracking process and, more particularly, to amethod and composition for use in the fluid catalytic cracking processusing a sulfur reduction additive composition.

2. Description of Related Art

Fluid catalytic cracking (FCC) is the largest refining process used forgasoline production with global capacity of more than 14.2 millionbarrels per day. The process converts heavy feedstocks such as vacuumdistillates, residues, and deasphalted oil into lighter products, whichare rich in olefins and aromatics. FCC catalysts are typically solidacids of fine-particles especially zeolites (synthetic Y-faujasite),aluminum silicate, treated clay (kaolin), bauxite, and silica-alumina.The zeolite content in commercial FCC catalysts is generally in therange of 5-40 weight %, or greater, while the balance is silica-aluminaamorphous matrix. Additives to the FCC process usually amount to no morethan 10% of the catalyst, and they are basically used to enhance octane,as metal passivators, SO_(x) reducing agents, CO oxidation and,recently, for gasoline sulfur reduction.

Stringent environmental regulations that target the reduction of thesulfur content of automobile gasoline and tailpipe emissions are beingenforced worldwide. Sulfur in gasoline increases SO_(x) emissions incombustion gases, reduces the activity of vehicle catalytic converters,and promotes corrosion of engine parts. The upper limit of sulfur ingasoline in the United States and the European Union has been set at 10parts per million (ppm) as a refinery average, and many other countrieshave also decreased the permitted sulfur specifications intransportation fuels.

A number of options are available for the reduction of sulfur ingasoline. The main options are hydrotreating the FCC feed, hydrotreatingproduct naphtha, lowering the end boiling point of FCC gasoline, and theuse of sulfur-reducing additives in FCC catalysts. The first two optionsare highly capital intensive. A disadvantage regarding the third optionis that the lowering of end boiling point will also reduce the octanenumber, in addition to reducing the yield of gasoline. From an economicpoint of view, the last option is the most desirable since this willselectively desulfurize the gasoline fraction without the need foradditional treatment. It has been reported that sulfur reduction by FCCadditives or catalysts offers economic advantages over the standardsolution-selective gasoline hydrotreating or hydrodesulfurizationmethods.

Various catalytic materials for effecting a sulfur reduction have beendeveloped for use during the FCC process. The sulfur reduction componentmay be a separate additive to the FCC catalyst or part of an FCC sulfurreduction catalyst. However, the levels of sulfur in gasoline are stillnot low enough to meet current and proposed regulatory requirements and,accordingly, are unacceptable.

Catalyst additives for the reduction of sulfur in FCC gasoline productswere proposed by Wormbecher in U.S. Pat. No. 5,376,608 and Kim in U.S.Pat. No. 5,525,210, the disclosures of which are incorporated byreference, using a cracking catalyst additive of an alumina-supportedLewis acid for the production of reduced-sulfur gasoline. It was alsodisclosed that the Lewis acid may comprise components and compoundsincluding Zn, Cu, Ni, Ag, Cd and Ga deposited on aluminum oxide.However, this system has not achieved significant commercial success.

Another composition is that disclosed in U.S. Pat. No. 6,036,847 toZiebarth et al., the disclosure of which is incorporated herein byreference, used 10 weight % of a mixture including particles of Znsupported on alumina and titania particles as an additive in thecracking of 2.7 weight % sulfur vacuum gas oil (VGO) feed. The resultsindicated that the combination of alumina-supported Lewis acid componentand titania-containing component resulted in greater sulfur reductionthan the use of either component alone.

Myrstad et al. in U.S. Patent No. 6,497,811, the disclosure of which isincorporated herein by reference, disclosed a composition of ahydrotalcite material impregnated with a Lewis acid, and optionally anFCC-catalyst, as a sulfur-reducing additive. The Lewis acid includedtransition metals elements and compounds, including Zn, Cu, Ni, Co, Feand Mn.

Another additive disclosed by Roberie et al. in U.S. Pat. No. 6,482,315,the disclosure of which is incorporated herein by reference, discloses acomposition comprising vanadium supported on a refractory inorganicoxide. When using 2 weight % vanadium-containing additive, a 33%reduction in gasoline sulfur was reported.

Various papers, published by Andersson, P. et al., Catalysis Today53:565 (1991), Beltran F. et al, Applied Catalysis Environmental 34:137(2001) and 42: 145 (2003), relate in only a very general manner to theconcept of the present invention.

Notwithstanding the reported sulfur-reducing catalysts, there remains aneed for effective and economical catalysts for reducing sulfur fromgasoline in a commercially sustainable manner.

Therefore, it is an object of the present invention to provide asulfur-reducing composition and a method for the use of same whichprovides a gasoline with a significantly lower sulfur level, whencompared to the sulfur reduction activity of a conventionally used FCCcatalyst in the FCC process.

SUMMARY OF THE INVENTION

The present invention provides additive compositions for reducing thesulfur content of FCC gasoline and processes using the compositions. Inone aspect of the present invention, the sulfur reduction additivecomposition comprises a support material having deposited on its surface(a) a first metal component from Group IIB of the Periodic Table and (b)a second metal component from Group III or Group IV of the PeriodicTable. The composition is most preferably made of a montmorillonite claysupport on which zinc and gallium or zinc and zirconium are impregnated.

In another aspect, the composition comprises a support material havingdeposited on its surface a metal component from Group III of thePeriodic Table. The composition is most preferably made of amontmorillonite clay support on which only gallium is impregnated.

Preferably, the support material is an amorphous or inorganic oxide suchas, for example, Al₂O₃, clays, or mixtures thereof. In certain preferredembodiments, the support material is montmorillonite clay.

The metal or metals are impregnated or dispersed on the surface of theclay particles by any suitable conventional process, e.g., the incipientwetness method.

The sulfur reduction additive composition is used as a separate additivein combination with the conventional fluid catalytic cracking catalyst,which is normally a faujasite, such as zeolite Y, to crack hydrocarbonfeeds in the FCC unit to produce low-sulfur gasoline and other liquidcracking products.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail below and withreference to the attached drawings in which:

FIG. 1 is a plot of the sulfur content of product gasoline fractionsobtained with a conventional FCC catalyst without any additive as areference material, and a mixture of the FCC catalyst with a commercialadditive, as a comparative material, versus percent conversion;

FIG. 2 is a plot of the sulfur content of product gasoline fractionsobtained with the reference material and the comparative material ofFIG. 1, and a base clay material used in additive compositions of thepresent invention, versus percent conversion;

FIG. 3 is a plot of the sulfur content of product gasoline fractionsobtained with a zinc impregnated-base material, the reference materialand the comparative material, versus percent conversion;

FIG. 4 is a plot of the sulfur content of product gasoline fractionsobtained with the reference material and the comparative material ofFIG. 1, and a zinc and zirconium impregnated base material, versuspercent conversion;

FIG. 5 is a plot of the sulfur content of product gasoline fractionsobtained with the reference material and the comparative material ofFIG. 1, and a gallium impregnated base material, versus percentconversion; and

FIG. 6 is a plot of the sulfur content of product gasoline fractionsobtained with the reference material and the comparative material ofFIG. 1, and a zinc and gallium impregnated base material, versus percentconversion.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, the sulfur content of an FCCgasoline is reduced to lower levels by the use of the additivecomposition of the invention mixed with a conventional FCC catalyst. TheFCC catalyst is preferably made of powder and generally possesses anaverage particle size in the range of 50-100 microns and a bulk densityin the range of 0.5-1.0 kg/L. It is preferred that the particle size,density, shape and mechanical strength of the catalyst additivecomposition of the present invention is the same as a conventional FCCcatalyst in which the composition is to be physically mixed.

The support material of the additive compositions of the presentinvention is preferably a montmorillonite clay possessing a surface areain the range of 150-350 m²/g. Clay material itself possessesconsiderable capacity to reduce sulfur in gasoline fraction. However,the reduction in the benzothiophene fraction is typically minimal. Itwas observed that the impregnation of only a Lewis acid component ontothe clay did not significantly increase either overall sulfur reductioncapacity or the reduction of benzothiophene.

It was also observed that use of an additive composition of the claymaterial that was impregnated with zinc and a metal from Group III ofthe Periodic Table, such as Ga, or Group IV, such as Zr, did furtherreduce the sulfur content of the gasoline fraction which wascatalytically cracked in the FCC unit. The clay material undergoes adrying step to produce shaped bodies suitable for use in the reductionof sulfur from gasoline and it can also be used alone as the gasolinesulfur reduction additive composition.

It was further that use of an additive composition of the clay materialthat was impregnated with a metal from Group III of the Periodic Table,such as Ga, reduced the sulfur content of the gasoline fraction that wascatalytically cracked in an FCC unit.

In order to further illustrate the present invention and the advantagesthereof, the following specific examples are presented. The examples arepresented as specific embodiments of the claimed invention. It should beunderstood, however, that the invention is not limited to the specificdetails set forth in the examples. The examples illustrate thepreparation and evaluation of the catalytic activity specific additivecompositions for reducing sulfur content of a catalytically crackedgasoline fraction in a typical FCC unit.

The conventional cracking catalyst particles preferably contain at leastone cracking catalyst component which is catalytically active for thecracking of hydrocarbons in the absence of added hydrogen. The crackingcatalyst component can comprise a zeolite, a non-zeolite molecularsieve, a catalytically active amorphous silica alumina species, or acombination thereof. In certain embodiments, the cracking catalystcomponent is a Y-type zeolite selected from the group consisting of Y,USY, (described in U.S. Pat. No. 3,293,192, which is incorporated hereinby reference), REY and RE-USY (described in U.S. Pat. Nos. 3,867,307 and3,676,368, both of which are incorporated herein by reference) andmixtures thereof. The cracking catalyst particles can also contain oneor more matrix components such as clays, modified clays, alumina, andthe like. The cracking catalyst particles can also contain a binder suchas an inorganic oxide sol or gel. The cracking catalyst particlesgenerally contain at least 5 weight %, and in certain embodiments about5 weight % to about 50 weight %, of the cracking catalyst component.

EXAMPLES

Micro activity test (MAT) evaluations of FCC catalyst/additive mixtureswere carried out according to ASTM method D-3907, at a reactiontemperature of 510° C. and a injection time of 30 seconds for acatalyst-to-oil ratio between 3 to 5, to obtain a conversion to gasolineof 55 to 75% of the original feed. The feed used was a vacuum gas oil ofArabian light crude origin. The sulfur content of this feed was 2.5weight percent. Other properties of this feed are shown in Table 1. Thesulfur content of the gasoline fraction was measured by GC-SCD. Forcomparison purposes, the sulfur content of the gasoline fraction wascalculated at 71% conversion level. The montmorillonite clay wascalcined in air at 550° C. to remove physically adsorbed water.Calcinations at 550° C. did not result in a significant increase in thesurface area.

TABLE 1 Properties of vacuum gas oil (VGO). Property Value Density(g/cc) 0.882 API 29.1 Carbon (wt %) 85.08 Hydrogen (wt %) 12.08 Sulfur(wt %) 2.46 Nitrogen (wt %) 960 Initial Boiling Point (° C.) 214 FinalBoiling Point (° C.) 588

Example 1

Sulfur Content of Gasoline Fraction Obtained with Use of a ConventionalFCC Catalyst.

A steamed, conventional, commercial FCC zeolite catalyst, a typical lowRE-USY type available from any FCC catalyst supplier, was evaluated inthe MAT according to ASTM D 3907. FIG. 1 shows the plot of gasolinesulfur content versus percent conversion obtained with only theconventional catalyst without any additive composition. This sulfurcontent is taken as a reference.

Example 2

Sulfur Reduction with a Commercially Available Additive Composition.

A commercial sulfur reduction additive composition generally availablefrom a catalyst supplier, for example, Albemarle, CCIC, Englehard, GraceDavison, or Intercat, labeled as comparative additive composition in thetables, was added (10 weight %) to the same steamed conventional FCCcatalyst, namely, low RE-USY, as in Example 1 and was tested in MATunder the same conditions as in Example 1. The sulfur content of thegasoline fraction in this Example 2 is compared to the reference sulfurcontent in FIG. 1.

At a conversion to gasoline of 71%, the overall sulfur reductionachieved, including benzothiophene, was 16%. Table 2 lists the sulfurcontent of the gasoline fraction for all the additive compositions.

Example 3

Sulfur Reduction of FCC Naphta with the Base Material of the PresentInvention.

To measure the sulfur reduction capability of the support material,montmorillonite clay itself was mixed with a conventional catalyst, atypical RE-USY type available from any FCC catalyst supplier, andevaluated in MAT. The results obtained, which are shown in FIG. 2, werecompared with the reference. Montmorillonite demonstrated a significantsulfur reduction capability. As reported in Table 2, the sulfur contentof the product gasoline fraction was reduced by 21%.

Example 4

Results Obtained by Use of Zinc-Impregnated Clay.

An additive composition was prepared by impregnating 3 weight % Zn onmontmorillonite clay by the incipient wetness method. A quantity of 10weight % of this composition was mixed with the same commercialcatalyst, a typical low RE-USY type, available from any FCC catalystsupplier, as in Example 1 and tested in MAT. FIG. 3 compares the sulfurcontent of gasoline obtained by using the composition of Example 4 withthat obtained with use of the reference catalyst and the composition ofExample 3. It is seen that sulfur reduction capability of thiscomposition of Example 4 is similar to the composition of Example 3. At71% gasoline conversion, product gasoline sulfur was reduced by 21%, asreported in Table 2.

Example 5

Results Obtained by Use of Clay Impregnated with Zinc and Zirconium.

An additive composition of the invention was prepared by impregnating 3weight % Zn and 1 weight % Zr on montmorillonite clay by the incipientwetness method. A quantity of 10 weight % of this composition was mixedwith the same commercial catalyst, a typical low RE-USY type, availablefrom any FCC catalyst supplier, as in Example 1 and tested in MAT. FIG.4 compares the sulfur content of gasoline obtained using the compositionof Example 5 with that obtained by use of the reference catalyst and thecomposition of Example 4. It is seen that sulfur reduction capability ofthis composition is higher than the composition of Example 4. At 71%conversion to gasoline, product gasoline sulfur was reduced by 40%, asreported in Table 2.

Example 6

Results Obtained by Use of Gallium-Impregnated Clay.

An additive composition of the invention was prepared by impregnating 3weight % Ga on montmorillonite clay by the incipient wetness method. Aquantity of 10 weight % of this composition was mixed with the samecommercial catalyst, a typical low RE-USY type, available from any FCCcatalyst supplier, as in Example 1 and tested in MAT. FIG. 5 comparesthe sulfur content of gasoline obtained using the composition of Example6 with that obtained by use of the reference catalyst and thecomposition of Example 3. It is seen that sulfur reduction capability ofthis composition is superior to the composition of Example 4. At 71%conversion, product gasoline sulfur was reduced by 38%, as reported inTable 2.

Example 7

Results Obtained by Use of Clay Impregnated with Zinc and Gallium.

An additive composition was prepared by impregnating 3 weight % Zn and 1weight % Ga on montmorillonite clay by the incipient wetness method. Aquantity of 10 weight % of this composition was mixed with the samecommercial catalyst, a typical low RE-USY type, available from any FCCcatalyst supplier, as in Example 1 and tested in MAT. FIG. 6 comparesthe sulfur content of gasoline obtained using the additive compositionof Example 7 with that obtained by use of the reference catalyst and theadditive composition of Example 4. It is seen that sulfur reductioncapability of this additive composition is higher than the additivecomposition of Example 4. At 71% gasoline conversion, product gasolinesulfur was reduced by 39%, as reported in Table 2.

TABLE 2 Sulfur content of gasoline fraction and percent reduction insulfur content Sulfur Additive Composition content % reduction ReferenceMaterial 659 0 (no additive composition) Comparative 553 16 Clay 523 21Zn/Clay 520 21 Ga/Clay 410 38 Zn—Zr/Clay 393 40 Zn—Ga/Clay 405 39

The compositions of the present invention and their methods of use havebeen described above; however, modifications will be apparent to thoseof ordinary skill in the art and the scope of protection for theinvention is to be defined by the claims that follow.

We claim:
 1. A fluid catalytic cracking (FCC) mixture comprising an FCCcatalyst and separate particles of sulfur reduction additive consistingof porous montmorillonite clay
 2. The mixture as in claim 1, wherein themontmorillonite clay has a surface area in the range of 150 m ²/g to 350m ²/g.
 3. The mixture as in claim 1, wherein the montmorillonite clay iscalcined in air at 550° C.